High speed digital integrated circuits are typically mounted on logic panels to interconnect the leads of the different IC's (integrated circuits). Each logic panel includes a core of insulative material and two conductive layers, each covering most of the surface of a corresponding face of the core. These layers are used to distribute various voltages and system ground directly to or close to each integrated circuit and are generally referred to as voltage and ground planes. IC's are generally plugged into machined sockets so the IC's lie over the voltage plane, and that side of the panel is referred to as the component side. The wires that interconnect selected socket pin terminals with plugged-in IC leads generally lie over the ground plane, and that side of the panel is referred to as the wiring side. Numerous decoupling capacitors are commonly mounted on the logic panel close to the integrated circuits, each capacitor extending between the voltage and ground planes to filter out noise. It is important that the connections between the capacitor terminals and the voltage and ground planes avoid the introduction of significant inductances. An inductance in series with a decoupling capacitor, and connecting the voltage and ground planes, would result in an LC resonance at a particular high frequency. A circuit formed on the logic panel cannot operate at frequencies near such a resonance, since operation near a resonant frequency would create unacceptable noise.
SMT (surface mounted) capacitors have become widely used to filter electrical noise in logic panels. The SMT's are commonly mounted on the component side of a logic panel beneath plug-in integrated circuits. One terminal of the capacitor lies on and is soldered to the voltage plane. The other terminal of the capacitor is soldered to a separate conductive trace that leads to a plated-through hole in the board, that connects to the ground plane on the wiring side of the board. Logic panels with such SMT capacitors have been found useful to frequencies up to about 90 MHz (megahertz), but are found to produce inductances that prevent their use above 100 MHz. For higher frequencies, designers have had to resort to stripline and microstrip boards where the etched conductive traces are designed to act somewhat like waveguides or transmission lines. Such stripline and microstrip boards have permanently etched circuit traces, are much more expensive to design and manufacture in small quantities, and do not easily allow for discrete wire connections (wherein any lead of any plug-in integrated circuit can be connected to any other lead of another integrated circuit, to permit circuit changeability).
SMT's are often soldered onto the logic panel, beneath plug-in integrated circuits, so they occupy a space that might otherwise be wasted and lie very close to the integrated circuit power connections. However, such capacitor mounting gives rise to problems. One problem is that solder flux is often trapped in the narrow gap between the SMT capacitor body and the metal foil conductive layer on the surface of the circuit board. Difficult cleaning techniques are required because even traces of flux residue can cause serious corrosion when exposed to humidity. Another problem is that SMT capacitors require expensive machines to place them on the circuit board and to solder them in place. SMT capacitors and connecting solder joints can also be broken or conductive traces cracked when the plug-in integrated circuits over them are pried out of the sockets. A single shorted capacitor renders the entire logic panel useless until repaired and damaged SMT capacitors are difficult to detect. A decoupling capacitor mounting arrangement which avoided the creation of appreciable inductances, to thereby enable logic panels to operate at higher speeds, would be of considerable value. Such a capacitor mounting arrangement which also protected the capacitors from harm, all in a system which enabled low cost placement and electrical connection of the capacitors, would be of considerable value.